Telephone intercept system



March 21, 1944. w. T. POWELL 2,344,634

' TELEPHONE INTERCEPT SYSTEM Filed Jail. 8, 1942 2 Sheets-Sheet 1.

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2 Sheets-Sheet 2 Filed Jan. 8, 1942 Hun wt? 9h Patented Mar. 21, 1944 TELEPHONE INTERCEPT SYSTEM Winfred T. Powell, Brighton, N. Y., assignor to The Stromberg-Carlson Telephone Manufacturing Company, Rochester, N. Y., a corporation of New York Application January 8, 1942, Serial No. 426,013

17 Claims.

This invention relates to telephone systems and more particularly to improvements in circuits for providing call intercept service in conjunction with the use of lines in an automatic telephone.

system.

It is one object of the present invention to" provide improved circui'tsof the character described, which are simple and economical and which function in a positive and reliable manner to intercept calls to one or more predetermined substations on one or more lines of the system, a

to automatically connect the intercepted 'calls to a common intercept trunk and then to apply to the calling line a special tone or tick-tick signal to inform the calling party that the called station is out of service, or the like.

Another object of the invention is to provide circuit arrangements so that the control of the call intercepting apparatus is effected through operation of the common ringing interrupter equipment in conjunction with an intercept interrupter equipment, controlled in synchronism.

It is a further object of the invention to provide circuits of the character described, so arranged that the operation to intercept a call, by

the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a conventional manner, with all of the contacts associated with a particular relay being illustrated as attached to this relay by means of a dotted line. The nega tive side of the common exchange battery is indicated by a minus sign in parentheses and the positive side of the exchange battery, which is usually grounded, is indicated by a positive symbol in parentheses.

While certain features of the invention are applicable to and useable with any type of party line telephone system, the specific embodiment of the invention has been shown in a form adapted connecting the calling subscriber to the common intercept trunk, is effective to initiate a timing mechanism which functions to automatically release the calling connection from the common intercept trunk after a predetermined time interval. r

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings and inpart pointed out as the description thereof progresses.

, In describing the invention in detail, reference will be made to the accompanying drawings in which like characters designate corresponding parts and in which:

Figure 1 illustrates one modification of the intercept circuit arrangement, controlled in part by ringing interrupters and intercept interrupters operating as will be described.

Figure 2 is a timing chart illustrating the time intervals during which the various ringing interrupter contacts and the various intercept interrupter contacts may be closed to provide proper operation of the system.

Figure 3 illustrates an alternate circuit arrangement in which harmonic relays are used in place of the common intercept interrupters.

For the purpose of simplifying the illustrations and facilitating the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawings having been made more with the purpose of making it easy to understand the principles and mode of operation than with for use with an automatic telephone system.

Furthermore, it is assumed that the invention is applied to a party line telephone system in which five different ringing frequencies are employed for selectively ringing the bells on a selected party line. It is also assumed that the lines in the particular system to which this invention is applied are divided circuit ringing lines, with live stations selected by ringing over one side of the line to ground and with five additional stations selected by ringing over the other side of the line to ground.

It is believed that the invention will be best understood by explaining the operation when a connection is made to the line circuit illustrated in Figure 1, assuming first that 16 cycle ringing current is applied to this line and second that the station which responds to 16 cycle ringing current has been disconnected and consequently the call must be routed to the common intercept trunk and the calling subscriber must be given a signal to this effect.

The five different ringing frequencies are indicated, in the upper left-hand portion of the Figure 1 drawing, as being applied through separate transformers and separate ringing lamps to normally open contacts of separate common ringing interrupters. The back contacts of these common ringing interrupters are connected through a common lamp to negative battery and this is for the purpose of providing a return circuit for tripping the ring when a call is answered during a silent interval.

Associated with these five ringing interrupters and in line therewith are shown five intercept interrupters indicated IIIS, I130, I142, I154 and 1166. These intercept interrupters are controlled by the same shaft that controls the ringing interrupter contacts, thus a cooperative relation between the operation of these ringing interrupters and intercept interrupter contacts can readily be. obtained. For example, referring to Figure ,2, it will be assumed that a 6 second cycle is used, with the ringing curtercept interrupter is closed for a short interval, but it will be noted that there is no overlap from.

any intercept interrupter into a period during which a non-corresponding ringing interrupter is.

applying ringing current to the associated ringing commons. e

A small portion of a link circuit is illustrated in Figure 1. It comprises a cut-in relay G1, a

ringing relay RI, a reversing relay RV, a

and contrip relay TR, a frequency selector necting terminals TL, RL and SL. It will be understood that the connection from the calling line to the called line is made through the link circuit, which may be a connector switch or the connecting mechanism of a relay type connector, by way of the tip line connector TL and the ring line connector RL, with the sleeve SL of the link applying positive battery to the sleeve terminal of the called line circuit for making this line busy and for operating the cut-off relay. After the called line is selected, it is usually the practice to dial a station selecting digit which operates the frequency selector for selecting the proper frequency for ringing the desired station. As illustrated, this frequency selector selects any one of the five frequencies indicated in response to dialing digits 1, 2, 3, 4 or 5. Furthermore, it is well known by those skilled in the art that a reversing relay RV, associated with the connector link, may be left in its normal position for ringing over the tip side of the line or it may be operated in response to a separate digit for ringing over the ring side of the line.

It is also well known by those skilled in the art how cut-in relay CI, is operated after the line is selected, how ringing relay RI is operated to ring the called line and how trip relay TR'is operated for releasing relay R1 to disconnect the called line from the ringing circuit and for connecting it through to the talking circuit, including the calling line.

It will now be assumed that the line circuit illustrated in Figure 1 is selected by the connector link and that 16 cycle ringing current is selected and that the station responsive to 16 cycle current on this line has been disconnected. When ringing interrupter RI [6 closes itsfront contact a circuit is closed from the right hand terminal of the secondary Winding of the 16 cycle transformer, through lamp iii, front contact if of the 16 cycle ringing interrupter, terminal l6 and frequency selector wiper or contactor 11, Winding of trip relay TR, back contact l8 of relay RV,'front contact 19 of relay RI, front contact 25) of relay CI, tip side of the connecting link TL, terminal 2!, intercept terminal T (to which intercept terminal XI is cross connected as indicated by the dotted line), condenser 22, rectiher 23, upper winding of intercept line relay Al, positive side of battery and thence through the battery to the negative side and to the other terminal of the ringing transformer.

This current from the link connector terminal TL also passes out over the tip side of the called line, through the station ringers, ring side of the called line, connecting terminal RL, front contact 24 of relay CI, front contact 25 of relay RI, back contact 26 of relay RV, to positive battery and thence through the battery and to the other terminal of the ringing transformer. Since .formation operator called for the desired in formation.

Ringing current through the upper winding of relay AI; as above described, is effective to operatethis relay during the half cycles when the ringing impulses, over the above described circuit and through the upper winding of relay AI, are positive. During the other half cycles, when the ringing current impulses are negative, the

current will flow through the lower winding of relay AI and not through its upper winding.

. Consequently, because of the oppositely poled rectifier and the double wound coil of relay Al, the alternating current flowing over this circuit will hold relay Al operated during the ringing interval without any chatter.

Recalling that intercept interrupter IIIG is normally closed during the ringing period of the 16 cycle current, a circuit may be traced from the positive side of battery, contact of intercept interrupter III6, terminal l6 and cross connection to terminal YI, front contact 21 of relay Ai, back contact 28 of connecting relay Bl, winding of relay Bl, back contact 29 of relay Bi and back contact 30 of common lockout relay L0 to negative battery. Relay BI is operated over this circuit and closes a locking circuit for itself which extends from positive battery now connected to the sleeve terminal S of the called line, cross connection to terminal Zl, front contact of "make-before-break combination 28 of relayBi,

winding of relay BI, front contact of make-before-break combination 29 of relay BI and winding of relay L0 to negative battery. Relay Lil is thus inserted in series with the winding of relay BI, relay L0 operates and opens its back contact 30 which removes negative battery from the operating circuits of all of the connecting (B) relays. This lockout arrangement prevents the operation of more than one B relay at any one time.

The operation of relay BI closes a circuit for operating slow to operate relay S0 which extends from positive battery, front contact 3| of relay Bl, back contact 32 of the make-before-break combination or relay RT and winding of relay S0 to negative battery. The operation of relay S0 closes an obvious operating circuit, at its front contact 33, for operating ringing trip relay RT. The operation of relay RT opens up the circuit of relay S0 at back contact 32, which allows relay SE] to release and relay RT is now locked operated by way of its make-before-break front contact 32 to positive battery at front contact 3| of relay BI. This means that when relay Bl operates to-connect the calling line to the common intercept trunk, relay St. is operated and very shortly thereafter releases. During its operation-positive battery by way of its front contact 34 is connected through front contact 35 of relay Bl to terminal XI and over the remainder of the previously described ringing circuit, which includes trip relay TR of the link. Consequently this momentary operation-of relay Sil is sufiicient to trip the ring but is not long enough to operate the usualbattery feed relay provided in connector link circuits, which have reverse battery contacts for reversing the battery to the calling With relay RT locked operated, a circuit is -closed through its front contact 36 'for'operating relay 'ITlin series with resistance coll'3'l. It will be noted that relay TT2 is short-circuited at this time by back contact 38 of relay TII. When relay TTI operates, however, back contact-38 is opened and relay 'I'I2 is operated in series with resistance coil 39. The operation of relay 'I'IZ closes a circuit at its front contact 40 which short-circuits and releases relay TTI. The release of relay TTI closes its contact 38 for shortcircuiting and releasing relay 'I'IZ. This intermittent operation of relays TTI and TT2 continues at a fairly rapid rate for intermittently energizing the left-hand winding of transformer coil TF over a circuit including front contact 4| and resistance coil 42. This sets up an inductive effect in the right hand winding of coil TF which is extended through condenser 43, resistance coil 44 and front contact 35 of relay BI to the tip terminal TL of the connector link and thence to the calling line by way of front contact 20 and back contact l9, recalling that relay BI is released .when the tripping operation is effected in the connector link.

The calling subscriber, hearing this tick-tick signal, releases the connection including the conneotor link. When this disconnection takes place, positive battery is removed from terminal S of thecalled line and the associated terminal Z! of the intercept connecting circuit, which is effective to open the locking circuit and effect the release of relay BI. Since this locking circuit includes the winding of relay L0, this latter relay is released and negative battery is again connected to all of the connecting relays in readiness for another intercept circuit operation.

It will be apparent that, since relay AI is not tuned to any particular frequency, it will be operated when the line to which it is connected has any of the five frequencies applied thereto. However, it requires correspondence between the frequency which is applied to the line and the closure of the associated intercept interrupter contact for the operation of the. associated B relay. For example, if 30 cycle ringing current is applied to the line, over the above described connection, relay AI will operate as before, but in this instance relay Bl will not operate because its operating circuit through front contact 21 of relay Al extends by way of cross connection Yl to intercept interrupter III6 and this interrupter is not closed in correspondence with ringing interrupter RI30. Furthermore, with the illustrated cross connection between terminal Yl and the #16 intercept interrupter IIIB, ringing over this line with any otherfrequency will operate relay Al but will not'operate relay BI It will be understood that terminal XI may be cross connected to the ring side of the line (terminal R) for operation when ringing'current is applied to the ring side of the called line. A second intercept circuit, comprising relays A2 and B2 and its terminals X2, Y2 and Z2, is illustrated to indicate the interlock between these intercept circuits for preventing the operating of more than one at any one time. This interlock between intercept circuits is effected, as above described, by energizing lockout relay L in series with any B relay which is operated and by arranging the contacts of the common lockout relay so that it opens up the energizing circuits for all B relays. It will be understood that as many of these intercept circuits, comprising A and B relays, may be provided as is necessary to take care of the maximum number of intercept stations to be handled.

Since it is possible that two or more lines may beselectedat the same time and the intercept stations thereon dialed, it will be understood that ringing current may be effective to operate two or more A relays at the same time, but only one calling line will be connected to the common intercept trunk at the same time. It is desirable to provide a time disconnect arrangement to automatically release a calling subscriber from the common intercept trunk so that it will not be tied up for an abnormal length of time, thus delaying its selection by other waiting calls. This time disconnect arrangement may be applied to the circuit of Figure l in the same way that it is applied to the circuit of Figure 3, the operation of which will now be explained.

Referrring to Figure 3, the connecting terminals of a connector link circuit are illustrated in the upper left-hand portion of this figure. These terminals comprise tip, ring and sleeve contacts TL, RL and SL and connect to the line circuit in the same manner as already explained in connection with Figure 1. Each intercept circuit comprises a line relay and a connecting relay, three sets of these intercept circuits being shown comprising relays Al and BI for circuit #1, A2 and B2 for circuit #2 and AIG and BIG for circuit #16. It will be assumed that 16 circuits may be accommodated by the common intercept trunk, that is, 16 substations may have their service disconnected and connected by way of these intercept circuits to the common intercept trunk at some time during the interval between directory issues.

' The cross connections in this modification are made from the L terminals, such as terminal LI, to either the tip or the ring side of the line, depending upon the side of the line that the intercepted station was on. Terminal Zl is cross connected to the sleeve terminal of the line circuit. It will be understood that terminals L2 and Z2 and other similar terminals, up to and including L16 and 216, may be cross connected to other lines having intercepted stations thereon. In this modification, it is not necessary to use a separate relay combination, comprising an A relay and a B relay, when 2 or more stations on the same line are placed on intercept. It is only necessary to cross connect the terminals similar to VI and WI to a relay similar to BPI, as illustrated, and then connect terminal Yl to the proper one of the five common leads leading to frequency relays FBI 6, FR30, FR42, FR54 and FRGB. Now connect one or more of the terminals XYI, XYZ, XY 3, XY4 to separate ones of the five common leads. Since there are four extra Y terminals (XYI, KY2, KY3 and KY4) associated with relay BP'l and since this relay is a direct repeater of relay B l, five stations on the same line can be placed on intercept by the use of only one set of relays such as Al, BI and BPl.

Although not illustrated in Figure 3, it will be understood that the common ringing interrupter arrangement and the frequency selector of the link for selecting the various frequencies are the same as disclosed in Figure l. The intercept interrupters are not required in this modification.

It will now be assumed that terminal Ll of the first intercept circuit is cross connected to the tip side of the illustrated line, that terminal Z! is cross connected to the sleeve terminal of this line and that terminal Yl is cross connected to the common conductor leading to frequency relay FRIB. It will be understood that these five frequency responsive relays are selectively responsive to the five different frequencies selected by the frequency selector as illustrated in Figure 1.

. Although it forms no part of the present invention, a gas relay; is connected in series with each A relay of each intercept circuit, these gas relays, being designated. GRZ, GRIG, with the first one bein labeled gasrelay l. 'A common gas relay GRC is connected in series with the five frequency responsive relays. The function of these gas relays is to simulate the condition of the party line which has substations connected thereto, with a gas relay in each ringer circuit. These gas relays serve the purpose of permitting sufiicient current to flow to ring the associated bells and to offer a high impedance to noise currents for reducing noise in the telephone circuits due to grounded ringers.

. With the above assumptions, when the illustrated line is called and 16 cycle generator is applied to the tip side of the line, generator current flows through the cross connection to terminal Ll, through condenser 45, rectifier 46, upper winding of relay A] and the gas relay to positive battery. This circuit is completed during the positive half cycles of the ringing current and during negative half cycles, the circuit is completed through lower winding of relay All and rectifier 4?; Therefore, relay Al is operated without chatter by the alternating ringing current flowing over this circuit. It will be apparent that this current alsoflows out over the called line but, since it is assumed that the 16 cycle station is out of service, no bell will ring and it becomes necessary to give the calling subscriber a signal to the effect that the station is out of service.

The operation of relay AI closes a circuit for operating relay Bi, which extends from positive battery, front contact 58 of relay Al upper winding of relay Bl, back contact of make-beforebreak combination 49, back contact 50 of relay Lil, back contact 55 of relay RT, back contact 52 of relay SA and resistance 53 to negative battery. Relay Bl closes a first locking circuit for itself including the winding of relay L0, front contact 49 and upper winding of relay BI. The opening of back contact 70 disconnects the operating circuit of relay Bi and the closure of the front contact of this make-before-break combination efiects the operation of relay L which, at back contact 50 opens up the common circuit to negative battery for all B relays, thus preventing the operation of more than one of these relays at any one time.

The operation of relay Bl extends the ringing circuit, by way of front contact 55 and cross connection Y1, to the winding of relay FRIG, the ringing circuit being completed through condenser and gas relay GRC, by way of positive battery and thence through the battery to the other side of the ringing source. Relay FRIB is operated in response to the 16 cycle ringing current which is being applied to the called line. It will be understood that, when this line is selected and some other frequency is applied, none of the frequency selecting relays of the common intercept trunk will operate because the only one that is connected to the ringing circuit is FRIG and it does not respond to any of th other selected frequencies.

The opening of the lower back contact 49 of relay Bl opens up the series circuit through all other 13 relays. This is to prevent any other B relay being maintained in its operated position in the event that two or more attempt to operate at exactly th same time. In other words-,,relay B'l has preference, with other B relays being next choice in operation byway of the series circuit extending from the #1 'B' relay to the #16 B relay.

With relay FRI G operated, a circuit is closed for operating common relay CM which extends from positive battery, front contact 56 of relay L0, contact 51 of relay FRIB, and, lower winding of relay CM to negative battery. Relay CM closes a locking circuit for itself extending from positive battery on the sleeve conductor of the called line circuit, cross connection ZI, front contact 58 of relay Bl, lower'winding of relay BI, back contact 59 of slow acting relay SA, front contact 60 and upper winding of relay GM to negative battery. This circuit locks relays BI and. CM to the sleeve conductor ofv the called line.

A circuit is now closed for operating slow to operate relay SD which extends from positive battery, back contact 6| of relay RT, front contact 52' of relay CM and winding of relay S0 to negative battery. A circuit is nowclosed for operating relay RT which extends from positive battery through front contact 63 of relay S0. Relay RT closes a locking circuit for itself which extends from positive battery, front contact 64 of relay CM, front contact 65 and winding of relay RT to negative battery. Relay RT effects the release of relay S9 .by opening its back contact 6|. Thus, contact H of relay Si] is momentarily closed to trip the ring in the link.

The tick-tick relays TTI and TT2 are now operated over a circuit which extends through front contact SI of relay RT. The operation of these tick-tick relays is the same as already described in connection with Figure 1 and need not be repeated here. They function to intermittently apply positive battery to the transformer TF, through which a tick-tick signal is superimposed on the calling line.

When the calling subscriber hangs up the receiver, the release" of the connector link opens up the sleeve circuit leading to terminal Zl, which effects the release of relay Bl, which in turn restores the intercept circuit to normal so that another connection may now be made to the common intercept trunk.

From the above it will be apparent that the application of a ingingfrequency to a called line which corresponds to the connection of jumper Y! (or Y2 up to YI6, inclusive, of the other intercept circuits), effects the operation of the correspondirg frequency responsive relay for completing the above described locking circuit for-relays'similar to BI and CM. The application of any other frequency to this. jumper connection is ineffective to operate a frequency responsive relay and consequently the intercept circuit connected to the called line does not function'to seize the common intercept trunk.

A time release feature has been applied to the circuit shownin Figure 3 and comprises a dashpot relay, arepeater of the dash-pot relay DPR and a slow acting. relay SA. As above explained, relay RT operates when the common intercept trunk is seized. This closes a circuit for energizing the dash-pot relay which extends from positive battery,. back. contact 66 of relay SA, front contact 61 of relay RT and winding of the dash-pot relay to negative battery. The dashpot relay is adjustedto complete its operation in a predetermined time, say 15 seconds. If the calling party, hearing the tick-tick tone, releases before this 15-second interval, the circuits function as previously described. In the event that the calling party does not release before this interval, the complete operation of the dash-pot relay closes an obvious circuit for operating relay DPR and relay DPR. closes an obvious circuit for w operating relay SA. The operation of relay'SA opens up the energizing circuit of the dash-pot relay at back contact 66, which effects the release of the dash-pot relay,-followed by the sequential release of relays DPR and SA. With relay DPR released and before relay SA releases, the opening of front contact 68 while back contact 59 is open, opens up the holding circuit including relays CM and BI (01 the like). This effects the release of the connection from the common intercept circuit, which renders this common circuit available for another call. Itwill be noted that when a connection is released from the common intercept trunk in this manner, this particular connection will not attempt to seize the intercept trunk again because the ringing has been tripped in the connector link which established the connection.

It should be noted that relay BPI is a direct repeater of relay BI and consequently the contacts of relay BPI can as well be placed on relay Bl by providing a relay designed to carry this additional number of contacts.

It is also to be noted that, although the'operation of one connecting relay, such as relay Bl, locks out all others this does not prevent the operation of some other B relay associated with an intercept station, because the common generator frequencies are staggered as indicated in the timing chart of Figure 2. i

Having described an intercept system as par ticularly adaptable for selective type communication service in partyline ringing systems, it is desiredto have it understood that this form is selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and it is to be further understood that various modifications, adaptions and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention exceptjas limited by the appended claims.

What I claim is: a 1

1. In a telephone system, party lines, means for extending connections to said party lines, a common interrupter, means including said come mon interrupter for intermittently applying ringing currents of difierent character to connections extended to said party lines for selectively ringing stations thereon, means responsive to the application of said ringing currents to said lines efiective in the event that the desired stations thereon are out of service for directing contemporaneous connections to a common intercept trunk, means for transferring one only of said contemporaneous connections to said common intercept trunk, and means forstoring the other contemporaneous connections.

2. In an intercept system for telephone party lines, generator means for selectively signalling stations on said lines, a common intercept trunk, individual intercept control relay units interposed between a plurality of party lines and said inter cept trunk one unit for each line, and generator controlled means associated with said intercept trunk and any one of said control relay units for connecting a call for any of a plurality of inter- -for extending connections from a calling line to said party lines, means including a common ringing interrupter for selectively applying ringing currents of difierent characteristics to a connection to any one of said party lines for selectively signalling the desired station thereon, common testing means including said ringing interrupter 'fordetermining whether or not the desired station is out of service, means for extending a connection intended for a station out of service to a common intercept trunk, and means for applying a special intercept signal to the calling line connection extended to said intercept trunk.

4. In a telephone system, party lines, means for extending connections from a calling line to said party lines, means including a common ringing interrupter for selectively applying ringing currents of different characteristics to a connection to'any one of said'party lines for selectively signalling the desired station thereon, common testing means including said ringing interrupter for determining whether or not, the desired station is out of service, means for extending a connection intended for a station out of service to a common intercept trunk, means for applying a special intercept signal to the calling line connection extended to said intercept trunk, and means for preventing the extension of more than one connection to said intercept trunk at any one time. a

5. In a telephone system, party lines, means for extending connections to said party lines, means including a common ringing interrupter for selectively applying ringing currents of different characteristics to a connection to any one of said lines for selectively signalling the desired station thereon, common testing means including said ringing interrupter for determining whether. or not the desired station is out of service, means for extending a connection intended for a station out of serviceto a common intercept trunk, means for applying a special intercept signal to the connection extended to said intercept trunk, means for preventing the extension of more than one connection to said intercept trunk at any one time, and means for automatically releasing an extended connection from said common intercept trunk after a predetermined time interval.

6. In an intercept system for telephone party lines, a common intercept trunk, a plurality of connecting units connected to said party lines, each of said connecting units comprising a line relay, and a connecting relay, means responsive to the application of signalling current to a plurality of said party lines for operating a plurality of said line relays, means including said line relays for efiecting the operation of one of said connecting relays, means controlled by the operation of one of said connecting relays for preventing the operation of any other of said connecting relays, and means controlled by the operation of one of said connecting relays for effecting a connection to said intercept trunk.

7. In an intercept system for telephone party lines, a common intercept trunk, a plurality of connecting relays connected tosaid party lines, means including a plurality of ringing interrupters operating at different time intervals for applying ringing current to said party lines and to the connecting relays connected thereto, a plurality of intercept interrupters operating at time intervals corresponding at least :in part to the time intervals of said ringing interrupters, and

:means responsive to correspondence between one of said ringing interrupters and one of :said intercept interrupters for effecting a connect-ionof one of said connecting relays to said intercept trunk.

8.1111 an intercept system ,for telephone party .lines, a common intercept trunk, a plurality of connecting relays connected to said party lines,

,means includinga plurality of ringing interrupt- .ers'operating at different time intervals for applying ringing cur-rent :to said party lines and to the connecting .relays connected thereto, a plurality of intercept interrupters operating at time intervals corresponding at least in part to the time intervals of said ringing interrupters, means responsive to correspondence between one of said ringin interrupters and one of said intercept interrupters for efiecting a connection of one of said connecting relays to said intercept trunk, and lock out means for preventing said correspondence effecting the connection of more than one connecting relay to said intercept trunk at anyone time.

9. In an intercept system for telephone party lines, .a common intercept trunk, a plurality of connecting relays connected to said party lines, means including a plurality of ringing interrupters operating at different time intervals for applying ringing current to said party lines and to the connecting relays connected thereto, a plurality of intercept interrupters operating at time intervals corresponding at least in part to the time intervals of said ringing interrupters, means responsive to correspondence between one of said ringing interrupters and one of said intercept interrupters for effecting a connection of one .of said connecting relays to said intercept trunk, lock out means for preventing said correspondence effecting the connection of .more than one connecting relay to said intercept trunk at any one time, and time control means for automatically releasing said one connecting relay from said intercept trunk whereby correspondence between said ringing and intercept interrupters is effective to connect another waiting connection to said intercept trunk.

10. In an intercept system .for telephone party lines, a common intercept trunk, a separate pair of individual intercept relays connected to terminals of each line from which a plurality of stations have been been removed from service, means efiective in case anyone of said plurality of stations is called for operating the associated pair of said intercept relays, means controlled by the operation of said pair of intercept relays for connecting the call for any one of said plurality of stations to said intercept trunk, and automatic means associated with said intercept trunk for applying a distinctive signal to a calling line connected to the intercept trunk whereby the calling party is signalled that the called station is out otf service.

11. In a telephone system, a hire, an intercept trunk, means for extending a call to said line and to said intercept trunk, locking means for maintaining said extended call in association with said intercept trunk, and time controlled means for automatically disassociating said extended call from said intercept trunk.

12. In a telephone system, a plurality of lines,

an intercept trunk, means for extending calls to said *lines and to said intercept trunk, locking means for maintaining an extended call in association with said intercept trunk, time controlled means .for automatically disassociating said extended call from said intercept trunk, and means controlled by said lockin means for preventing the extension of more than one call to said intercept trunk at any one time.

13. .In a telephone system, a line adapted to have a plurality of substations associated therewith, means for routing calls to said line from other lines, means for selectively applying separately characterized ringing voltages to said line for selectively signalling said substations, call intercepting means, means responsive to any of said characterized ringing voltages :for initiating operation of said call intercepting means, and means responsive to a particular characterized ringing voltage for completing the operation of said call intercepting means whereby the call is intercepted.

14. In a telephone system, a line adapted to have a plurality of substations associated therewith, means for routing calls to said line from other lines, means for selectively applying separately characterized ringin voltages to said line for selectively signalling said substations, call intercepting means comprising a circuit individual to said line and a circuit common to all of said lines, means responsive to any of said characterized ringing voltages for operating said individual circuit, and means responsive to a particular characterized ringing'voltage for operating said common circuit to intercept th call to said line.

15. In a telephone system including a called line and ringing apparatus for impressing ringing voltage on the called lin during any one of a plurality of time intervals, apparatus for routing a call ,from a calling line to a common intercept circuit only in the event ringing voltage is impressed upon said called line during a predetermined one of said time intervals, and means for applying a distinctive audible signal to said calling line only in the event that it is connected to said intercept circuit.

16. In a telephone system including a called line and ringing apparatus for impressing ringing voltage on the called line during any one of a plurality of time intervals, apparatus .for routing a call from a calling line to a common intercept circuit only in the event ringing voltage is impressed upon' said called line during a predetermined one of said time intervals, means for applying a distinctive audible signal to said calling line only in the event that it is connected to said intercept circuit, and time control means associated with said intercept circuit for automatically disconnecting said calling line from said intercept circuit.

17. In a telephone system, a calling line, a called party line, means for establishing a connection from said calling line to said called line and for transmitting any one of a plurality of distinctive ringing signals to said "party line for calling any one of the parties thereon, an intercept trunk associated with said called party line, means responsive to a particular ringing signal transmitted to said party line and trunk for applying a special intercept signal to said calling line.

WINFRED T. POWELL. 

